In different applications for automation engineering, the use of sensors or actuators via data buses for monitoring and controlling of processes has become very popular. Related cost advantages may be remarkable, in particular, because the complexity of the wiring and cabling may be reduced, at the same time improving the reliability of operation.
Indeed, the advantages of reducing the need for cabling and wiring have been considered to be so important that in some applications employing system components requiring an electrical power supply, in addition to the primary function of data transfer, a secondary function of providing electrical power through the data bus has been implemented too. This is the case with the AS-Interface bus, for example.
For actuators, such as valve sets, with relatively high power consumption, the “black power cable” next to the “yellow cable” of the AS-Interface bus provides a 24V floating DC supply which is fully isolated from the data signals. The “black power cable” in an AS-Interface bus is typically rated up to 8 A though the cable itself could handle more. With an improved design, currents higher than 8 A can be drawn, still complying with the AS-Interface specification regarding the amount of voltage drops in the network.
Unfortunately, part of the advantages gained by the reduced need for cabling or wiring are lost if a separate power cable is needed.